Electron discharge device of the magnetron type



Dec. 31, 1946. R. c. SCHMIDT ELECTRON DISGH'KRGE DEVICE OF THE MAGNETRONTYPE 2 Sheets-Sheet 2 Filed March 23, 1945 //l/L A/7'0/?. lioamr 6550/0110:

Patented Dec. 31, 1946 UNITED STATES PATENT OFFICE ELECTRON DISCHARGEDEVICE OF THE MAGNETRON TYPE Claims. 1

This invention relates to electron-discharge devices, such asmagnetrons, for example, and more particularly to tuning means for suchdevices.

One of the objects of the present invention is to provide novel andeilicient means for varying the frequency of the oscillations generatedby the device.

Another object of the present invention is to provide novel and reliableelectronic tuning means for such a device.

These objects and such other aims and objects of the present inventionas may hereinafter apffit pear will be best understood from thefollowing description taken in connection with the accompanying drawingsof embodiments of the invention herein presented for illustrativepurposes.

In the drawings Fig. 1 is a vertical section taken substantially throughthe center of an electron-discharge device comprising one illustrativeembodiment of the invention;

Fig. 2 is a section on line 2-2 of Fig. 1 showing a top plan view of aconcentric line through which oscillations are led out of the device andof a stub line comprising the tuning means, certain parts being brokenaway to show the interior construction; and

Fig. 3 is a sectional elevation of another illustrative embodiment ofthe tuning means.

In the drawings the invention is illustratively shown in its applicationto an electron-discharge device of the magnetron type, comprising anenvelope including a cylinder 2 closed at its ends by caps I and B,respectively, said caps being soldered to the ends of said cylinder 2 toform an hermetically sealed enclosure. Said cylinder 2 and caps I and imay be made of copper or other suitable electrically conductivematerial. A central annular projection B is formed upon the innersurface of said cylinder, to which are soldered a plurality of suitablyspaced, radiallydisposed plates or arms l0. Said arms In, cylinder 2 andcaps 4 and 6 constitute the anode structure of the device, and the innerends of said arms ill form anode faces for receiving electrons from acathode l2 supported centrally of said anode faces. Said plates mayconveniently be stamped from a plate of highly conductive copper.

Said cathode I2 is preferably of the indirectlyheated. thermionic typeprovided with an outer electrically conductive sleeve l4 coated withelectron-emissive oxides or other electron-emissive material. Itcontains a heater-wire of conventional construction, not shown, of whichthe end conductors l8 and I8 project centrally from the opposite end ofthe cathode. One of said conductors, the conductor ID, for example, maybe connected to said outer conductive cathode sleeve ll, the otherconductor It being insulated from said sleeve. The cathode I2 ispreferably supported by a cathode and heater-wire lead-in conductor 20,welded to the end of said conductor ii. A second lead-in conductor 22has its inner end welded to the free end of said conductor l8. Saidlead-in conductors 20 and 22, are connected to a suitable source ofvoltage, not shown, and are sealed in well-known conventional mannerthrough glass seals 24 and 26 at the outer ends of conductive pipes 28and 30. (See Fig. 1.) Light conductive shields 32, 34, hereinconveniently integral with said cathode sleeve II, are provided atopposite ends of the latter to prevent electron beams from beingprojected outwardly toward said end caps l and 6.

If such a device he placed between suitable pole pieces 38 and 38 toproduce a longitudinal magnetic field within the device and said devicebe energized, oscillations will be generated which may be led out of thedevice by a coupling loop Ill (see Fig. 2), extending into the spacebetween two of said anode arms lli. One end of said coupling loop I isconnected to the inner end of a conductive pipe 42 hermetically sealedthrough the wall of said cylinder 2, substantially midway between theendsof the latter, and its other end is connected to a conductor 44which extends through said pipe 42 and is sealed through a glass seal 46mounted at the outer end of said pipe 42.

Each pair of anode arms It forms with the portion of the projection 8between them an oscillating cavity or cavity resonator. A capacitanceexists between the cathode I2 and the end faces of said anode arms l0and also between the side walls of each resonator cavity 48. Theconductive path around each cavity is afforded by the side walls thereofand the portion of said pro- ,iection 8 between them, constitutes aninductonce. The anode structure is therefore so designed and spacedrelatively to the cathode that said inductances and capacitancesconstitute tuned circuits. It is desired that these circuits shall beresonant at a definite, predetermined frequency at which the device isto operate.

I shall now describe one illustrative embodiment of means in accordancewith my invention for varying the frequency of the oscillationsgenerated by the device. A coupling loop 50 extends into one of thecavity resonators 48. One end of said loop is connected to the inner endof an outer tubular conductor 52 having a reduced end auasea 3 sealedthrough the wall of the envelope, and the outer end of said loop isconnected to the inner end 01' a conductor I extending axially of saidtubular member. The conductor together with members capacitativelycoupled thereto and forming a high frequency extension of said conductor58, as described below, constitute with the tubular member 52, a coaxialline. The outer section El of the central conductor of the coaxial lineis sealed through a glass seal 51 carried in said tubular member 52.Said coaxial line is closed on by 9. Partition 68 at its outer end, sothat it forms a stub line. Said central conductor has incorporatedtherein electron-emissive means, said means herein consisting of twotubular cathodes comprising conductive sleeves 80 and 82. The sleeve 82is insulated from the end of conductor 50 and from a central hollowconductor 85 by insulating rings 84 of glass or other suitableinsulating material. The sleeve 62 is also insulated from the conductors65 and 5| by similar rings 84. The capacities which exist through therings 84 form low impedances for the high frequency currents and thuscause the members 56, 62, 65, B0 and Ii to act as the center conductorof the coaxial line. The outer surface of each cathode sleeve may beprovided with a coating 58 of electron-emissive material, such as theoxides of alkaline-earth metals. Preferably said coating will be in theform of a band encircling each of said sleeves Bil, 62. Herein, thecathodes are of the indirectlyheated. thermionic type, heaters 88 and I0being connected in series by conductor l2 and I4 with a battery 16.Energy is supplied to the two cathodes from a potential divider 18, onenegative pole of which being connected to said cathode sleeve 52 byconductor 82 through a resistance 88, the other negative pole beingconnected to said cathode sleeve 60 by conductor 84, through resistance88, the positive poles being connected by conductor 90 to said tubularconductor 52 acting as an anode. Contacts 92 and 94 engage resistances86 and 88. respectively, and serve to vary the voltage as will behereinafter more fully explained.

The coaxial line described above constitutes a reactance coupled to theoscillating circuit of the electron-discharge device by said couplingloop 50. Herein, when the cathode sleeves ill and B2 are energized, themaximum length of said coaxial line terminates at a: (see Fig. 2) andthe minimum length terminates at 1/, the distance d between the pointsa: and 1/ being equal to that is to say, to one-quarter of a 'wavelength when n is equal to one.

In accordance with my understanding of the operation of my invention,the oscillations generated in the device generate a standing wave in thetubular conductor 52 and a reactive impedance is reflected back into thetube which may be either inductive or capacitive, dependent upon thelength of the conductive line, and it is by varying the magnitude of theinductive or capacitive impedance by varying the length of the coaxialline, that the tuning of the device is effected.

When voltage is impressed upon the cathode Gil, an electron flow willradiate outwardly from the electron-emissive coating 88 encircling saidcathode to the inner wall of said tubular conductor 52. Similarly whenvoltage is impressed upon the cathode 62. an electron flow will radiatefrom the latters electron-emissive surface ll across to the surroundinginner wall of the tubular member conductor 52. Such an electron flowconstitutes a relatively low impedance which blocks the progress of theoscillations along said tubular conductor and thus limits the length ofthe concentric conductive line.

Referring more particularly to Fig. 2, means are thereindiagrammatically illustrated for moving the contacts 82 and 94 alOl'igthe resistances 88 and 88, respectively, said means hereinillustratively comprising a handle 98 on an insulating bar ill attachedto the two conductors 82 and 84. Assuming that the contacts 92 and 84are at the extreme left end (viewing Fig. 2) of their respectiveresistances 8i and 88, if said bar 88 be moved to the right (viewingFig. 2), more and more of the resistance 88 will be cut out of theenergizing circuit of the cathode 60 and more and more of the resistance85 'will be thrown into the energizing circuit of the cathode B2. Theelectron flow from the cathode B0 to the tubular conductor 52 will thusgradually increase while the electron flow from the cathode 62 to saidtubular conductor will gradually decrease, until, when the contact 98reaches the right end of resistance 86 (view Fig. 2), and the contact 94reaches the right end of the resistance 88. the electron flow from thecathode 60 will be at its maximum and the electron flow from the cathode62 will be at its minimum. Displacement of said contacts 92 and 94 fromthe right ends respectively to the left ends of said resistances 86 and88 respectively will gradually decrease the electron flow from thecathode 60 from its maximum to its minimum and gradually increase theelectron flow from the cathode 62 from its minimum to its maximum. It ismy present understanding of the operation of my invention that as. bythe adjustment of said contacts 92 and 8| the electron emission from onecathode is caused to predominate more and more over the electronemission from the other cathode, the coaxial line is lengthened orshortened according as the adjustment is such as to cause thepredominating electron emission to come from the cathode ill or from thecathode 62. It will thus be seen that the adjustment described furnishesan eilective and simple means for shifting the location of theterminating impedance produced by the electron flow from the line a: tothe line 11 and vice versa, thus to vary the length of the coaxial lineand correspondingly to vary the frequencies of the oscillationsgenerated by the device throughout the adjustment range of said coaxialline.

In the illustrative embodiment of the invention shown in Fig. 3, atubular conductor iflll is hermetically secured in the wall I02 of amagnetron which may and preferably will'be identical with the oneillustrated in Figs. 1 and 2. A central conductor IIM extends axially ofsaid tubular conductor Ill and an extension I 05 thereof is sealedthrough a glass seal "l6 closing the other end of said tubularconductor. The other end oi said conductor IM terminates in a. loop I08located in one of the cavity resonators I III of said magnetron, thefree end of said loop I" being connected to the inner end of saidtubular conductor Hill, said conductor Hi4, its extensions and saidtubular conductor lllil forming a concentric line. A cathode H2 ismounted on said central conductor I as an extension thereof and isinsulated therefrom and from the hollow conductor III! by insulatingrings I I3. Here likewise the capacities through the rings III cause themembers Ill, 2 and III! to act as the central conductor of a coaxialline. Said cathode is preferably of the indirectly-heated, thermionictype provided with an outer, electrically conductive sleeve Ill coatedwith electron-emissive oxides or other suitable electron-emisslvematerial, preferably in the form of a band lit encircling said sleeveIll. A heater coil III is contained within said cathode 2, one end ofsaid coil being connected by a conductor I20 with one pole of a batteryI22. the other end of said coil being connected by a conductor I24 withthe other pole of said battery- Said conductors I20 and I24 arehermetically sealed through an insulating button I28 of glass formingthe outer end wall of said central conductor I05. Said cathode isenergized by a battery I28 or other suitable source of energy. Thepositive pole of said battery is connected by a conductor Ilil to thewall of said tubular conductor ltlil. The battery has connected acrossit a potentiometer I32. An adiustable contact I on said potentiometer isconnected to the inner wall of said cathode M2 by a conductor I36 sealedthrough said insulating button I26. Said tubular conductor I00 and theinner assembly of the coaxial line are closed oil by a partition I38 atthe outer end so as to form a stub line. The maximum length of saidcoaxial line terminates at a: and the minimum length terminates at u,the distance d between the points a: and 1! being equal to which isone-quarter of a wave length when n is equal to one. Said coaxial lineconstitutes a reactance coupled to the oscillatory circuit of theelectron-discharge device by said coupling loop I08.

Referring to Fig. 3, it will be apparent that movement of the adjustablecontact ill to the right in said Fig. 3 will gradually increase theelectron flow from the cathode to said tubular conductor 52 whilemovement oi. said contact along said resistance in the oppositedirection will gradually decrease the flow of electrons from saidcathode to said tubular conductor 52. These changes in the magnitude ofthe electron flow T vary the reflected inductive or capacitive impedancein the tubular conductor I00 and thus either increase or decrease thelength of the coaxial line according as said electron flow is increasedor decreased. This, in turn, through said coupling loop I08 producescorresponding changes in the frequencies of the device.

I am aware that the present invention can be embodied in other specificforms without departing from the spirit or essential attributes thereof,and I therefore desire the present description 20 be considered in allrespects as illustrative and lot restrictive, reference being had to theappended claims rather than to the aforesaid description to indicate thescope of the invention.

What is claimed is:

l. tn electron-discharge device comprising a cathode, an anode structurespaced from said cathode and incorporating a cavity resonator, a tubularconductor, a second conductor extending axially through said tubularconductor and constituting a coaxial line therewith, said coaxial linebeing coupled to said cavity resonator, electron-emissive meansconnected to said second conductor through means having a low impedanceto high frequency currents, and means connected intermediate saidelectron-emissive means 6 and said tubular conductor for impressing avoltage therebetween, whereby said coaxial line may be effectivelyterminated at said electron-emissive means.

2. An electron-discharge device comprising a cathode, an anode structurespaced from said cathode and incorporating a cavity resonator. a tubularconductor, a second conductor extending axially through said tubularconductor and constituting a coaxial line therewith, said coaxial linebeing coupled to said cavity resonator, electron-emissive means mountedin said second conductor and connected thereto through means having alow impedance to high frequency currents, and means connectedintermediate said electron-emissive means and said tubular condoctor forimpressing a voltage therebetween, whereby said coaxial line may beeilectiveiy terminated at said electron-emissive means.

3. An electron-discharge device comprising a cathode, an anode structurespaced from said cathode and incorporating a cavity resonator, a tubularconductor, a second conductor extending axially through said tubularconductor and constituting a coaxial line therewith, said coaxial linebeing coupled to said cavity resonator, and electron-emissive meansmounted in said second conductor and connected thereto through meanshaving a low impedance to high frequency currents, and means connectedintermediate said electron-emissive means and said tubular conductor forimpressing a variable voltage therebetween, whereby said coaxial linemay be eilectively terminated at said electron-emissive means.

4. An electron-discharge device comprising a cathode, an anode structurespaced from said cathode and incorporating a cavity resonator, a tubularconductor, a second conductor extending axially through said tubularconductor and constituting a coaxial line therewith, said coaxial linebeing coupled to one end of a loop in said cavity resonator, the otherend of said loop being connected to said anode structure,electron-emissive means connected to said second conductor through meanshaving a low impedance to high frequency currents, and means connectedintermediate said electron-emissive means and said tubular conductor forimpressing a voltage therebetween, whereby said coaxial line may beeffectively terminated at said electron-emissive means.

5. An electron-discharge device comprising a cathode, an anode structurespaced from said cathode and incorporating a cavity resonator. a tubularconductor, a second conductor extending axially through said tubularconductor and constituting a coaxial line therewith, said coaxial linebeing coupled to said cavity resonator, two cathodes spacedlongitudinally of said conductor and connected thereto through meanshaving a low impedance to high frequency currents, and meansintermediate said two cathodes, respectively, and said tubularconductors for impressing a variable voltage therebetween, connectedwhereby said coaxial line may be efiectively terminated at eithercathode.

6. An electron-discharge device comprising a cathode, an anode structurespaced from said cathode and incorporating a cavity resonator, a tubularconductor, a second conductor extending axially through said tubularconductor and constituting therewith a coaxial line coupled to saidcavity resonator, electron-emissive means connected to said secondconductor through means having a low impedance to high frequencycurrents, means connected intermediate said electron-emissive means andsaid tubular conductor for impressing a voltage therebetween to createan impedance across said coaxial line, and including means for varyingthe eiiectlve position of said impedance lengthwise of said tubularconductor to vary the length of said coaxial line and the frequencies ofsaid device.

7. An electron-discharge device comprising a cathode, an anode structurespaced from said cathode and incorporating a cavity resonator, a tubularconductor, a second conductor extending axially through said tubularconductor, said tubular conductor and said second conductor constitutinga coaxial line coupled to said cavity resonator, a cathode connected tosaid second conductor through means having a low impedance to highfrequency currents, means connected intermediate said eiectron-emissivemeans and said tubular conductor for impressing a voltage therebetweento create an impedance across said coaxial line, and including means forvarying the voltage impressed between said cathode and said tubularconductor to vary the efl'ective position of said impedance lengthwiseof said tubular conductor to vary the length of said coaxial line andthe frequency 01' the device.

8. An electron-discharge device comprising a cathode, an anode structurespaced from said cathode and incorporating a cavity resonator, a tubularconductor, a second conductor extending axially through said tubularconductor, said tubular conductor and said second conductor constitutinga coaxial line coupled to said cavity resonator, two cathodes connectedto said second conductor through means having a low impedance to highfrequency currents, means connected intermediate said cathodes and saidtubular conductor for impressing a voltage therebetween to create animpedance across said coaxial 8 line, and including means for varyingrelativeli to each other the voltages impressed between sak two cathodesrespectively and said tubular conductor to vary the eil'ective positionof said impedance lengthwise oi said tubular conductor and the frequencyof the device.

9. An electron-discharge device comprising a cathode, an anode structurespaced from said cathode and incorporating a cavity resonator, s tubularconductor, a second conductor extending axially through said tubularconductor, said tubular conductor and said second conductor constitutinga coaxial conductive line coupled to said cavity resonator, a cathodemounted in said second conductor and connected thereto through meanshaving a low impedance to high frequency currents, means connectedintermediate said cathode and said tubular conductor for impressing avoltage therebetween to create an impedance across said coaxial line.and including means for varying the voltage impressed between saidcathode and said tubular conductor to vary the eitectiv position of saidimpedance and the frequency of the device.

10. An electron-discharge device comprising a cathode, an anodestructure spaced from said cathode and incorporating a, cavityresonator, a transmission line, including a pair of conductors, coupledto said cavity resonator, one of said conductors being provided with anelectron-emissive portion, and means, connected intermediate saidelectron-emissive portion and the other of said conductors, forimpressing a voltage therebetween, whereby a flow of electrons may beinstituted between said electron-emissive portion and said last-namedconductor to short circuit said transmission line.

ROBERT C. SCHMIDT.

Certificate of Correction Patent No. 2,413,385.

December 31, 1946.

ROBERT C. SCHMIDT It is hereby certified that errors appear in thenumbered patent requiring correction as follows:

grinted specification of the above olumn 6, line 61, claim 5, after theword "means insert connected; line 63, strike out connected; and thatthe said Letters Patent should be read with these corrections thereinthat the same may conform to the record of the case in the PatentOfiice.

Signed and sealed this 25th day of March, A. D. 1947.

LESLIE FRAZER,

First Assistant Omission of Patents.

tron-emissive means and said tubular conductor for impressing a voltagetherebetween to create an impedance across said coaxial line, andincluding means for varying the eiiectlve position of said impedancelengthwise of said tubular conductor to vary the length of said coaxialline and the frequencies of said device.

7. An electron-discharge device comprising a cathode, an anode structurespaced from said cathode and incorporating a cavity resonator, a tubularconductor, a second conductor extending axially through said tubularconductor, said tubular conductor and said second conductor constitutinga coaxial line coupled to said cavity resonator, a cathode connected tosaid second conductor through means having a low impedance to highfrequency currents, means connected intermediate said eiectron-emissivemeans and said tubular conductor for impressing a voltage therebetweento create an impedance across said coaxial line, and including means forvarying the voltage impressed between said cathode and said tubularconductor to vary the efl'ective position of said impedance lengthwiseof said tubular conductor to vary the length of said coaxial line andthe frequency 01' the device.

8. An electron-discharge device comprising a cathode, an anode structurespaced from said cathode and incorporating a cavity resonator, a tubularconductor, a second conductor extending axially through said tubularconductor, said tubular conductor and said second conductor constitutinga coaxial line coupled to said cavity resonator, two cathodes connectedto said second conductor through means having a low impedance to highfrequency currents, means connected intermediate said cathodes and saidtubular conductor for impressing a voltage therebetween to create animpedance across said coaxial 8 line, and including means for varyingrelativeli to each other the voltages impressed between sak two cathodesrespectively and said tubular conductor to vary the eil'ective positionof said impedance lengthwise oi said tubular conductor and the frequencyof the device.

9. An electron-discharge device comprising a cathode, an anode structurespaced from said cathode and incorporating a cavity resonator, s tubularconductor, a second conductor extending axially through said tubularconductor, said tubular conductor and said second conductor constitutinga coaxial conductive line coupled to said cavity resonator, a cathodemounted in said second conductor and connected thereto through meanshaving a low impedance to high frequency currents, means connectedintermediate said cathode and said tubular conductor for impressing avoltage therebetween to create an impedance across said coaxial line.and including means for varying the voltage impressed between saidcathode and said tubular conductor to vary the eitectiv position of saidimpedance and the frequency of the device.

10. An electron-discharge device comprising a cathode, an anodestructure spaced from said cathode and incorporating a, cavityresonator, a transmission line, including a pair of conductors, coupledto said cavity resonator, one of said conductors being provided with anelectron-emissive portion, and means, connected intermediate saidelectron-emissive portion and the other of said conductors, forimpressing a voltage therebetween, whereby a flow of electrons may beinstituted between said electron-emissive portion and said last-namedconductor to short circuit said transmission line.

ROBERT C. SCHMIDT.

Certificate of Correction Patent No. 2,413,385.

December 31, 1946.

ROBERT C. SCHMIDT It is hereby certified that errors appear in thenumbered patent requiring correction as follows:

grinted specification of the above olumn 6, line 61, claim 5, after theword "means insert connected; line 63, strike out connected; and thatthe said Letters Patent should be read with these corrections thereinthat the same may conform to the record of the case in the PatentOfiice.

Signed and sealed this 25th day of March, A. D. 1947.

LESLIE FRAZER,

First Assistant Omission of Patents.

